This invention relates to a reflection member and a liquid crystal display device using the same.
Recently, liquid crystal display (LCD) devices have come into wide use for personal computers, television receivers, word processors, mobile phones, etc. The LCD devices are required to be much higher in performance, compact in size, with low power consumption and cost. In order to comply with such requirements, research and development is in progress with reflection type LCD devices to utilize incident ambient light by reflection as a light source, and hybrid (reflection and transparence) type LCD devices with both light reflection and transparent functions as a light source.
It is quite important how effectively incident ambient light is utilized to illuminate a display screen of LCD devices in the case of light reflection. Thus, a reflection member used in the LCD device is designed to effectively utilize incident ambient light from all angles to achieve optimal reflection.
As shown in FIG. 8, for instance, a reflection member 1, such as a reflective pixel electrode used for an LCD device, includes convex prominences 2 formed on its surface as light scattering elements which each are 3 xcexcm to 20 xcexcm in diameter and 0.3 xcexcm to 1.2 xcexcm in height. The centers of convex prominences 2 form hexagonal lattices with parallel vectors of an angle of 60xc2x0 defined between adjacent convex prominences. The hexagonal lattices are regularly disposed in a constant distance. The regular disposition makes the reflection characteristic optimum because the convex prominences 2 scatter light and flat portions between them perform the specular reflection. Their optical interference, however, causes coloring.
For the purpose of avoiding such coloring, as shown in FIG. 9, the convex prominences 2 are provided at random, for instance, to collect scattering light in a limited region or to strengthen the intensity of scattering light in a specific observation direction.
The reflective pixel electrode 1 shown in FIG. 9, however, increases specular reflection regions so that it cannot provide the LCD device with a sufficiently bright display. In addition, since a light source image is reflected from the display surface and an observer moves it out of his viewing field, i.e., he or she avoids such a reflected image, the specular reflection regions do not practically contribute to improve the display brightness and he or she sees the display surface becoming dark. In short, the area of the specular reflection regions in the reflection member 1 depends on the distance between the convex prominences 2.
Now, sectional views of regions A, B and C in FIG. 9 are shown in FIGS. 10, 11 and 12, respectively. The distance between the adjacent convex prominences 2 is about 10 xcexcm in region A, which has a small specular reflection area. In the case of region B, however, the distance between the convex prominences 2 is about 8 xcexcm, so that overlapping, adjacent convex prominences 2 make their slope gentle and components in the vicinity of the specular reflection area increase.
The convex prominence 2 shown in FIG. 12 is about 12 xcexcm apart from its adjacent convex prominences 2, so that flat regions are made between adjacent convex prominences 2 and the specular reflection regions increase. Thus, in order to make the specular reflection regions small in size, i.e., to avoid coloring, it is necessary to increase the existence rate of an appropriate distance between the adjacent convex prominences 2.
It is, accordingly, an object of the present invention to provide a reflection member with little coloring but desirable reflection characteristics and an LCD device using such a reflection member.
According to one aspect of the present invention, a reflection member includes a plurality of light scattering elements with substantially the same shapes which are distributed at lattice points determined by rotating parallel vectors of hexagonal lattices. Since such a distribution reduces two-dimensional regular dispositions of scattering elements, coloring resulting from optical interferences can be significantly suppressed. Distances between light scattering elements can also be kept constant to obtain optimal slope angle distributions. An LCD device using the light scattering elements can achieve a bright display with significant uniformity.